A multiwire proportional chamber system for monitoring low momentum beam in accelerators

A diagnostic is being developed at the Los Alamos Neutron Science Center (LANSCE) for the purpose of identifying low momentum beam tails in the linear accelerator. These tails must be eliminated in order to maintain the transverse and longitudinal beam size. Instead of the currently used phosphor camera system, this instrument consists of a multiwire proportional chamber (MWPC) front end coupled to an EPICS compliant VME-based electronics package. Low momentum tails are detected with a resolution of 5 mm in the MWPC at a high dispersion point near a bending magnet. While phosphor is typically not sensitive in the nano amp range, the MWPC is sensitive down to about a pico amp. The electronics package will process the signals from each of the MWPC wires to generate an array of beam currents at each of the lower energies. The electronics will have a wideband analog front end, active antialias filter, and high-speed analog to digital converter for each wire. Data from multiple wires will be processed with an embedded digital signal processor and results placed in a set of VME registers. An EPICS application will assemble the data from these VME registers into a display of beam current vs. beam energy (momentum) in the LANSCE control room. This display will update at least once per second, but will be a representation of the real time signal processing results from the electronics package.